This invention pertains to a chemical-mechanical polishing system that can be used for the polishing of substrates such as semiconductor substrates, metallurgical samples, memory disk surfaces, magnetic heads, optical components, lenses, wafer masks, and the like.
In a typical chemical-mechanical polishing (CMP) system, a silicon wafer, semiconductor, or other such substrate to be polished is placed in direct contact with a rotating polishing pad. During the polishing process, the polishing pad is rotated while a downward force is maintained against the back of the substrate to cause the front of the substrate to contact the polishing pad. An abrasive and chemically reactive solution, referred to as a chemical-mechanical polishing composition or slurry, is applied to the polishing pad during the polishing (also referred to as planarization) of the substrate. The polishing composition often is comprised of an abrasive, an oxidizing agent, a liquid carrier, and other useful additives. The polishing composition assists the polishing process by both mechanically abrading and chemically reacting with the surface of the substrate. The polishing process is facilitated by the rotational movement of the polishing pad relative to the substrate while the polishing composition is provided to the substrate/polishing pad interface.
Polishing is continued in this manner until the desired material on the substrate is removed and the substrate surface is planar. Tailoring the polishing composition to meet the polishing requirements of a particular substrate (e.g., removing the desired material on the substrate as quickly as possible while minimizing surface imperfections, defects, corrosion, and erosion) is crucial to the success of a CMP process.
Many polishing compositions have been designed and disclosed as especially useful for particular CMP processes. For example, U.S. Pat. No. 5,244,534 discloses a polishing composition, containing alumina, hydrogen peroxide, water, and either potassium or ammonium hydroxide, which is useful to remove tungsten from a substrate at predictable rates with little removal of the underlying insulating layer. U.S. Pat. No. 5,209,816 discloses a polishing composition, comprising a solid abrasive material, hydrogen peroxide, perchloric acid and water, which is useful for polishing aluminum. U.S. Pat. No. 5,340,370 discloses a polishing composition, for polishing tungsten or titanium nitride, comprising silica, potassium ferricyanide, water, and optionally potassium acetate. U.S. Pat. No. 5,769,689 discloses the synergistic combination of amines and water-soluble salts in low concentrations in polishing compositions for polishing certain substrates. U.S. Pat. No. 4,789,648 discloses a polishing composition comprising alumina abrasives in conjunction with sulfuric, nitric, and acetic acids and deionized water. Other polishing compositions for use in CMP processes are described in U.S. Pat. Nos. 4,956,313, 5,137,544, 5,157,876, 5,354,490, and 5,527,423.
Although many polishing compositions for CMP processes have been developed and disclosed in the literature, there remains a need for further polishing compositions, particularly a chemical-mechanical polishing system suitable for effectively polishing a metal substrate. The invention provides such a polishing system and a method of using the polishing system to polish a substrate. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.
The invention provides a chemical-mechanical polishing system for a substrate comprising (a) a liquid carrier, (b) a polishing pad and/or an abrasive, (c) a per-type oxidizer, and (d) an additive. The additive is of the formula 
wherein R1 is a phosphono group, a carboxyl group or a salt thereof, R2 is a phosphono group, a carboxyl group or a salt thereof, and n is an integer from 1 to 50. The invention also provides a method of polishing a substrate comprising (a) contacting a substrate with the aforementioned polishing composition and (b) abrading at least a portion of the substrate to polish the substrate. When the substrate is a nickel-containing substrate, the additive additionally can be either 1,2,4-triazole or piperazine.